Volatile compounds of Chinese Luzhou flavoured liquor distilled from grains fermented in 100 to 300 year-old cellars

Evolution of fermented grain yeast communities in strong-flavored baijiu and functional validation of yeasts that produce superior-flavored substances

BACKGROUND

Baijiu is a well-known alcoholic beverage in China and the quality is determined by various microorganisms during the fermentation process. Yeast is one of the most important microorganisms in the fermentation of baijiu. It has a strong esterification capacity and also affects the aroma.

RESULTS

High-throughput sequencing results showed that the fermented grains (jiupei) during baijiu production were mainly composed of eight highly abundant yeast species. The species and abundance of yeasts changed significantly with the fermentation process. The flavor of 30 yeast strains in the jiupei was determined by a sniffing test and gas chromatography-mass spectrometry (GC-MS). The strain with the highest flavor substance content (2.34 mg L-1), named YX3205, was identified as Clavispora lusitaniae. Tolerance results showed that C. lusitaniae YX3205 can tolerate up to 15% (v v-1) ethanol. In a solid-state simulated fermentation experiment, the content of 24 flavor substances was significantly increased in the fortified group, and the total ester content reached 4240.73 μg kg-1, which was 2.8 times higher than that of the control group.

CONCLUSION

The present study demonstrated the potential of C. lusitaniae YX3205 to enhance the flavor of baijiu, thereby serving as a valuable strain for the improvement of the flavor quality of baijiu. © 2024 Society of Chemical Industry.

Chinese Baijiu: The Perfect Works of Microorganisms

Chinese Baijiu is one of the famous distilled liquor series with unique flavors in the world. Under the open environment, Chinese Baijiu was produced by two solid-state fermentation processes: jiuqu making and baijiu making. Chinese Baijiu can be divided into different types according to the production area, production process, starter type, and product flavor. Chinese Baijiu contains rich flavor components, such as esters and organic acids. The formation of these flavor substances is inseparable from the metabolism and interaction of different microorganisms, and thus, microorganisms play a leading role in the fermentation process of Chinese Baijiu. Bacteria, yeasts, and molds are the microorganisms involved in the brewing process of Chinese Baijiu, and they originate from various sources, such as the production environment, production workers, and jiuqu. This article reviews the typical flavor substances of different types of Chinese Baijiu, the types of microorganisms involved in the brewing process, and their functions. Methods that use microbial technology to enhance the flavor of baijiu, and for detecting flavor substances in baijiu were also introduced. This review systematically summarizes the role and application of Chinese Baijiu flavor components and microorganisms in baijiu brewing and provides data support for understanding Chinese Baijiu and further improving its quality.

The prokaryotic community, physicochemical properties and flavors dynamics and their correlations in fermented grains for Chinese strong-flavor Baijiu production

Fermented grain (FG), a complex and unique ecosystem, is the main microbial habitats, biochemical reaction system and direct source of flavor compounds for the Chinese strong-flavor Baijiu (CSFB) production. However, the dynamics of physicochemical properties, prokaryotic community and flavor compounds of FGs during the long-term fermentation process are still not completely clear. Here, the above topics on FGs in the actual production process were comprehensively studied by using a combination of physicochemical analysis, GC-MS detection and Illumina HiSeq sequencing methods. The whole fermentation process could be divided into two stages including early (0-25d) and the later stage (25-60d) based on the dynamics of FG physicochemical properties and the changes of prokaryotic community diversity. A total of 41phyla and 364 genera were detected, and 9 of them were dominant genera in FG complex ecosystem, including Lactobacillus, Pediococcus, Ochrobactrum, Bacillus etc. Among them, the dynamics of 29 top10 genera in FGs were mainly influenced by the starch and total acid, followed by NH₄⁺ and ethanol, and 7 genera (hubs, e.g., Clostridium, Methanosaeta, Bacillus, etc.) of them may play important roles in FG ecosystem stability. A total of 71 volatiles including 33 esters, 14 alcohols, 9 fatty acids, 5 phenols, and 10 other compounds were detected in the FGs, and most of them formed in the early stage. Some important flavor substances (e.g., ethyl octanoate, 3-methylbutanol, hexanoate, etc.) increased in the later stage. Moreover, the formation of some flavor compound might require multiple microbes involved. For instance, ten of the top10 genera, including Lactobacillus, Clostridium, Methanosarcina, Sedimentibacter, Bacillus, etc., were significantly and positively correlated with four important esters. This study may help to clarify the complex correlations among prokaryotic community, physicochemical properties and flavors, allow the improvement of CSFB quality by using bioaugmentation and/or controlling environmental factors, and shed more light on the ecological rules guiding community assembly in FGs.